In certain countries, changes have recently been made to regulations governing the safety of four-wheel-drive vehicles. In these countries, it is now required that braking of at least two wheels be guaranteed even in the event of failure of part of the hydraulic brake feed circuits. The purpose of these requirements is to ensure safer, more reliable braking of the tractor, even in the event of component breakdown, while at the same time allowing braking of each rear wheel individually for more effective steering, which is presently a common design feature on tractors. The Japanese market, for example, only approves tractors of over 35 km/h if two wheels can be braked even in the event of failure of a hydraulic brake feed system pipe (or component).